code: def conlltags2tree(
      sentence,
      chunk_types=("NP", "PP", "VP"),
      root_label="S",
      strict=False,
  ):
      """
      Convert the CoNLL IOB format to a tree.
      """
      tree = Tree(root_label, [])
      for word, postag, chunktag in sentence:
          if chunktag is None:
              if strict:
                  raise ValueError("Bad conll tag sequence")
              else:
                  # Treat as O
                  tree.append((word, postag))
          elif chunktag.startswith("B-"):
              tree.append(Tree(chunktag[2:], [(word, postag)]))
          elif chunktag.startswith("I-"):
              if (
                  len(tree) == 0
                  or not isinstance(tree[-1], Tree)
                  or tree[-1].label() != chunktag[2:]
              ):
                  if strict:
                      raise ValueError("Bad conll tag sequence")
                  else:
                      # Treat as B-*
                      tree.append(Tree(chunktag[2:], [(word, postag)]))
              else:
                  tree[-1].append((word, postag))
          elif chunktag == "O":
              tree.append((word, postag))
          else:
              raise ValueError(f"Bad conll tag {chunktag!r}")
      return tree
  
imports: import re
  from nltk.metrics import accuracy
  from nltk.tag.mapping import map_tag
  from nltk.tag.util import str2tuple
  from nltk.tree import Tree
label_desc: Use image node_id 6 for calling a global function with example usage: conlltags2tree(sentence, chunk_types, root_label, strict) and returns: tree